Descriptions

The floating ice shelf of Petermann glacier interacts directly with the ocean and is
thought to lose at least 80% of its mass through basal melting. Based on three opportunistic
ocean surveys in Petermann Fjord we describe the basic oceanography: the circulation
at the fjord mouth, the hydrographic structure beneath the ice shelf, the oceanic heat
delivered to the under‐ice cavity, and the fate of the resulting melt water. The 1100 m deep
fjord is separated from neighboring Hall Basin by a sill between 350 and 450 m deep.
Fjord bottom waters are renewed by episodic spillover at the sill of Atlantic water from the
Arctic. Glacial melt water appears on the northeast side of the fjord at depths between
200 m and that of the glacier’s grounding line (about 500 m). The fjord circulation is
fundamentally three‐dimensional; satellite imagery and geostrophic calculations suggest a
cyclonic gyre within the fjord mouth, with outflow on the northeast side. Tidal flows
are similar in magnitude to the geostrophic flow. The oceanic heat flux into the fjord
appears more than sufficient to account for the observed rate of basal melting. Cold,
low‐salinity water originating in the surface layer of Nares Strait in winter intrudes far
under the ice. This may limit basal melting to the inland half of the shelf. The melt rate and
long‐term stability of Petermann ice shelf may depend on regional sea ice cover and
fjord geometry, in addition to the supply of oceanic heat entering the fjord.